 Reduction 2 ScF 3 + 3 Ca  2 Sc + 3 CaF 2

1. ◆ ■ ◆ ■ □ ■ □ ◆ ◆ ■ ◆ ■ □ □ □ ◆ ■ ◆ □ ■ □ □ ◆ ■ ■ □ □ ■ ■ ◆ □ ■ □ □ ■ ◆ ◆ □ ■ □ □ MIG29 10 20 30 40 50 60 70 80 90 100 JCPDS # 04-0787 JCPDS # 17-0412 JCPDS # 14-0428 ◆: Al ■: Al3Sc □: Al4Ca JCPDS # 04-0787 JCPDS # 17-0412 JCPDS # 14-0428 ◆: Al ■: Al3Sc □: Al4Ca JCPDS # 17-0714 JCPDS # 05-0629 JCPDS # 20-0234 ◆: Sc ×: CaSc2O4 ○: Sc2O3 Intensity, I (a.u.) Intensity, I (a.u.) 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 Angle, 2θ/ degree Angle, 2θ/ degree *Determined by X-ray fluorescence analysis. Thermodynamic analysis Experiment Experiment TIG weld Sc2O3 (+ Al + CaCl2) Ta crucible Stainless steel reaction capsule Stainless steel sheet Ca shots Ti sponge Results Results Before exp. After exp. Ag cathode Ag cathode × 2.5 × × ◆ Intensity, I (a.u.) × × × × × 1 cm × Voltage, E / V × × ○ × × × × × × × ◆ × × × × × × × × × × × × 1 cm 2.0 i = 0.5 A t = 7200 s T = 1173 K 1.5 0 2500 5000 7500 Time, t / sec aDetermined by X-ray fluorescence analysis. Conclusion Angle, 2θ/ degree Future study Calcium Aluminum Scandium Al3Sc Al4Ca PRODUCTION OF SCANDIUMAND Al-Sc ALLOY BY USING CaCl2 MOLTEN SALT Masanori Harata*, Hiromasa Yakushiji, Toru H. Okabe *Institute of Industrial Science, The University of Tokyo, *Graduate Student, Graduate School of Engineering, The University of Tokyo Introduction ・Applications ・Conventional process ・Resource ・What is Scandium? Al-Sc alloys Sc is the 31stmost abundant element in the earth’s crust, with a crustal abundance of 22 ppm.  Conversion into fluoride: 973 K Sc2O3 + 6 HF  2 ScF3 + 3 H2O Thortveitite (Sc,Y)2Si2O7 Minerals such as Thortveitite contain a large amount of Sc. However, such minerals are not used as a source of Sc because they are scarce. Rare Earth Elements  Reduction 2 ScF3 + 3 Ca  2 Sc + 3 CaF2 1873 K Baseball bat Sc2O3 is converted into ScF3 because it is thermodynamically stable. Further, it is difficult to reduce Sc2O3 to metallic Sc even by using Ca as a reductant. Table Chemical composition of Thortveitite ・Disadvantages Sc is one of the rare earth elements (RE). Bicycle ・Properties of Sc Metal halide lamp The production cost is high because an expensive reaction apparatus is required for handling the fluoride. Table Minerals containing Sc Contamination from the crucible cannot be prevented due to the high-temperature reaction. Others Catalysts, Laser crystals ・Purpose of this study Currently, Sc is produced in the form of oxide (Sc2O3) from rare earth ores or as a byproduct of uranium mill tailings. To develop a new process that can produce Sc metal orAl-Sc alloy directly from Sc2O3 at temperatures lower than those used in the conventional process. Currently, Sc is mainly used as an alloying element for Al alloy. Recently, Ni smelting has changed froma pyrometallurgical process to a hydrometallurgical process that can recover a large amount of Sc2O3 at a low cost. ・Lightweight ・Chemically reactive ・Expensive Al-Sc alloy is expected to be used as a structural material for aircraft etc. ・Sc2O3 is one of the most stable oxides on earth Metallothermic Reduction Molten Salt Electrolysis Experimental temperature (1273 K) ・Anode  Reduction: Sc2O3 (s) + 3 Ca (g)  2 Sc (s) + 3 CaO (s) Potential lead (Ni wire) 0 C + x O2- → COx + 2x e- Stainless steel tube 4 Ag + O2 = 2 Ag2O ・Cathode  Reduction and alloying: Sc2O3 (s) + Al (l) + 3 Ca (g)  Al-Sc alloy (l) + 3 CaO (s) -200 Sc2O3 + 6 e- → 2 Sc + 3 O2- Rubber plug C + 1/2 O2 = CO C + O2 = CO2 ・Overall reaction -400 Ar inlet 3/2 Fe + O2 = 1/2 Fe3O4 Sc2O3 + C → 2 Sc + COx 4/3 Al + O2 = 2/3 Al2O3 -600 Standard Gibbs energy of formation, DGﾟf /kJ mol-1 Reaction chamber Ti + O2 = TiO2 Table Theoretical decomposition voltage -800 Ni reference electrode 4/3 La + O2 = 2/3 La2O3 2 Mg + O2 = 2 MgO Heater -1000 2 Ca + O2 = 2 CaO CaCl2-Sc2O3 molten salt -1200 4/3 Sc + O2 = 2/3 Sc2O3 4/3 Y + O2 = 2/3 Y2O3 Carbon electrode (Anode) -1400 300 500 700 900 1100 1300 Fe crucible Temperature, T / K Fig. Ellingham diagram of selected oxides. Al (or Ag)-Sc alloy (Cathode) Ceramic insulator Experimental temperature Ca contamination of Al-Sc alloy could be prevented by controlling the potential between the anode and the cathode. Fig. Schematic illustration of experimental apparatus for molten salt electrolysis. Fig. Schematic illustration of experimental apparatus for the metallothermic reduction experiment. As a preliminary experiment, Y2O3 was used instead of Sc2O3, and the production of Ag-Y alloy by the electrolysis of CaCl2-Y2O3 molten salt was investigated. Temperature, T’ / ºC Table Experimental conditions for the metallothermic reduction Electrolysis Mole percent Sc Fig. Phase diagram for the Al–Sc reaction Reduction temperature: T = 1273 K Holding time: t' = 6 hr XRD analysis (a) Feed: Sc2O3, Reductant: Ca A complex oxide (CaSc2O4) was formed and reduction was incomplete. Currently, Sc2O3 reduction is an ongoing experiment. (b) Feed: Sc2O3, Reductant: Ca, Collector metal: Al Sc2O3 was successfully reduced to metallic Sc and alloyed in situ to form Al-Sc liquid alloy during the reduction. It was difficult to separate the metal phase from the salt phase. It was demonstrated that Ag-Y alloy could be produced by the electrolysis of CaCl2-Y2O3 molten salt. The electrolysis cell must be improved to prevent the contamination of the molten salt by Fe. (c) Feed: Sc2O3, Reductant: Ca, Collector metal: Al, Flux: CaCl2 Phase separation was improved by using CaCl2 as a flux. However, excess Ca reductant remained in the Al4Ca phase. ・Metallothermic reduction Development of a new technique for preventing Ca contamination of Al-Sc alloy. Conclusion EPMA analysis ・Molten salt electrolysis Improvement of electrolysis cell to prevent Fe contamination. Investigation of the reaction mechanism of CaCl2–Sc2O3 molten salt. Development of a new direct production process of Sc or Al-Sc alloy by molten salt electrolysis. Al-Sc alloy was directly produced from Sc2O3 by using Al as the collector metal; however, excess Ca reductant remained in the alloy sample.